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In the given figure, AB || CD || EF. If AC = 7 cm, AE = 14 cm and BF = 20 cm, then DF is equal to:

In the given figure, AB || CD || EF. If AC = 7 cm, AE = 14 cm and BF = 20 cm, then DF is equal to: Mid-Point Theorem, Concise Mathematics Solutions ICSE Class 9.
  1. 7 cm

  2. 14 cm

  3. 10 cm

  4. 16 cm

Mid-point Theorem

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Answer

Given, AB || CD || EF, AC = 7 cm, AE = 14 cm and BF = 20 cm.

Let the length of DF be x cm.

According to equal intercept theorem,

If a transversal makes equal intercepts on three or more parallel lines, then any other line cutting them will also make equal intercepts.

From figure,

⇒ AE = AC + CE

⇒ 14 = 7 + CE

⇒ CE = 7 cm.

Since, OA makes equal intercept, so OB will also make equal intercepts.

∴ BD = DF = x (let)

From figure,

⇒ BF = BD + DF

⇒ 20 = x + x

⇒ 2x = 20

⇒ x = 202\dfrac{20}{2} = 10 cm.

Hence, option 3 is the correct option.

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